Radio receiving apparatus



B. B. MINNIUM RADIO RECEIVING APPARATUS Original Filed Dec. 8. 1924 NME Patented May ll, 1926.

warren sra'ras Parent carton BYRlJN B. M INNIUM, OF CHICAGO, ILLINQIS, KSSIG-NQR TO WALTER H. HUTH, OF

' CHICAGO, ILLINOIS.

RADIO RECEIVING APPARATUS.

Original application filed December 8, 1924, Serial No. 754,501; Divided and this application file February 1, 1926.

cillation which, of course, may interfere with the proper operation ot the apparatus,

inasmuch as such action has a tendency to interfere with the incoming signal, or even to entirely blanket the incoming signal, so to speak, and thereby prevent the proper operation of the apparatus.

This application is a division of my core pending application, Serial No. 7 04:,501

filed December 8, 1924.

Generally stated, therefore, the ob ect of the invention is to provide a novel and mproved circuit arrangement for preventing it) the above mentioned oscillation in radio frequency amplifier circuits, which is sometimes called a. feed back of energy from the plate to the grid of the vacuum tube, and to thereby insure against any interference oi l8 this kind with the proper reception of the incoming signal.

More particularly, it is an ob ect of this invention to provide a pair of simultaneously variable connected condensers, aran ranged in shunt to the tuning inductance whereby two arms of a VVheatstone bridge may be simultaneously adjusted so that the capacities in these two arms maintain a substantially fixed ratio for all adjustments 8! thereof.

It is also an object to provide certain de tails and features of construction and combinations tending to increase the general efiiciency and the desirability of-a radio frequency amplifying arrangement of this particular character.

To the foregoing and other useful ends, the invention consists in the'matters hereinafter set forth and claimed, and shown in 4 theaccompanying drawings,in which:

Fig. 1 is a diagram of a radio receiving apparatus involving the principles offithe invention; I

Serial No. 85,295.

Fig. 2 is a simplified diagram, using the ordinary vVheatstone bridge arrangement, showing the theory and the mode or operation of the invention; and

Fig. 3 is a diagram showing the preferred form of the invention.

its thus illustrated, the hook-up or circult arrangement shownin Fig. 1 is in a general way an ordinary one, involving a two-stage radio-frequency vacuum tube amplification. The aerial 1 may be of any suitable character and is grounded through the pr mary 2 of the transformer or repeating coil, as shown. The secondary coil 3 has one terminal connected to the grid 4 of the first vacuum tube, and has-its other terminal connected to the condenser 5 of any suitable character. The other terminal of the condenser 5 is connected to the plate 6 01 the vacuum tube, and the filament 7 of the tube has its terminals connected to the batteries shown at the right of the diagram, in the ordinary manner. The second stage of amplification is of similar character, it will be seen, and a description of the circuit arrangement of one vacuum tube will be sulficlent, v

For, tuning purposes, two adjustable condensers 8 and 9 are connected in series be tween the terminals of the secondary coil 3, so that the capacityand inductance-are in parallel, as shown. In addition, a tap-10 is taken from one; terminal of the filament 7 and carried over to. the middle point 11 of the capacity. shunt thus formed in parallel with the secondary coil 3 of the transformer or repeating coil. The primary coil 12 of: the next transformer or re eating coil, oi the second stage of ampli cation, is connected in circuit as shown, so that the coil 3" is in the input circuit of the vacuum tube, while the coil .12 is in the output circuit of said tube.

3 With this arrangement there is a tendency toward oscillation, as previously stated, owing toa sort of feed back from the plate 6-to the grid 4, durin the reception of the radio frequency signa but with the arrangement shown, involving the use of capacities 5 and 8 and 9, and the capacity between the grid 4 and the plate 6, the harmful and undesirable oscillation is pre vented. As shown by the Wheatstone bridge arrangement in Fig. 2, there is capacity in each arm of the bridge, so that all four arms of the bridge contaln enough capaeity to prevent the said feed back of en.- ergy from the plate to the grid of the vacuum tube. With such an arangement, it is found that any electrical disturbance or voltage across the points 13 and 14 will have no effect upon the points 15 and 16 or input terminals. In other words, the Wheatstone bridge arrangement is balanced, so to speak, and the points 15 and 16 remain at the same potential, so far as any electrical disturbance across 13 and 14 is concerned. In this,

Wheatstone bridge arrangement, as shown, there is employed as one capacity for one arm or side of the. bridge the-grid-to-plate capacity 4 and 6, and the other three arms of the Wheatstone bridge have the condensers 5, 8 and 9 located therein, as shown and described, The capacities 8 and 9 are employed for tuning the input circuit of the vacuum tube, as these condensersare adjustable.

The condensers 8 and 9 can be separately adjustable, or they can be mounted on thesame shaft, or gearedtogether, as indicated in Fig. 3, whereby the motionof one is governed. by that of the other, so that the two condensers may be varied together by a single control, but preferably in such a way as to at least approximately maintain a constant capacity ratio.

In the arrangement shown in Fig. 3, the condensers 8' and 9' have their rotatable elements 18 and 19 mechanically connected together, as schematically shown by the dash line 20, so that a' single control means such as a knob or dial may be used to efi'ect the control of both condensers at once. Obviously this scheme of control is applied to each stage of the amplified system so that but a single control is used for each stage of amplification.

One advantage of the invention, therefore, is that its operation is independent of the voltage distribution along the coil 3, -that is to say, since the filament of the amplifier tube is connected to the physical center of the input capacity, as shown, it is therefore connected to the electrical center of the input circuit, and hence with this arrangement there is no danger that the variation in voltage distribution along the coil may upset the balance of theWheatstone bridge arrangement thus involved in the hook-up or circuit arrangement shown and describe which is illustrative of one form of the invention.

As a further advantage, it has been found that when two capacities are connected in series, the resultant capacity variation is so greatly increased over that .usually obtainable that the size of the inductance 3 may be greatly increased and the size of 8 and 9 correspondingly reduced and still cover the wave length range over which the circuit is ordinarily tunable. One advantage of this is that the voltage applied to the grid of the vacuum tube amplifier is much greater than is obtained by the-ordinary arrange ment, thus insuring greatly increased amplification for each stage.

It will be understood, of course, that in practice 1 the different repeating coils or transformers will be so arranged, relatively to each other, that they will not affect each other, inductively, thereby to insure against interferencebetween them. Furthermore, it will also be observed that with the circuit arrangement shown and described. in the grid of eachvacuum tube has no metallic connectionto the filament of the tube, and hence has no metallic connection to an source of direct current, and hence there 1s no possibility of any such source impressing its voltage on the grid. With this circuit arrangement it is found that the tone quality is also improved, over that obtained with.

the ordinary'circuit arrangement, as the tone appears to be.clearerand better, which means better and more accuratereproduc tion.

The expression vacuum tube wherever used in this specification and claims is used in a generic sense and intended to include all devices of the type adapted to amplify radio frequency currents by a voltage control of a space current.

Having thus described the invention, what I claim as new and desire to be secured by Letters Patent is:

1. Radio frequency receiving apparatus comprising a vacuum tube having a filament, a grid and a plate, an inductance, a pair of simultaneously adjustable series c0n-' densers connected in effective shunt thereto and adapted to tune said inductance to rescapacity, and an inductance in the output circuit of said tube.

2. Radio frequency receiving apparatus comprising a vacuum tube having a filament', a grid and a plate, an inductance, a pair of series condensers connected in shunt thereto and adapted to tune said inductance to resonance with a signal, a tap from the cally connected together to maintain a subcommon point of said condensers to said filastantially fixed ratio for all adjustments ment, a lead from said grid to one end of thereof. A

said mductance, a connection from the plate In testimony whereof I hereunto affix my 5 to the other end of said. inductance, said consignature.

nection including a substantially pure capaov ity only, the said condensers being mechani- I ,BYRQN B. MINNIUM. 

